St. Petersburg Mining University (St. Petersburg, Russia):

Bolobov V. I., Professor, Doctor of Engineering Sciences, Senior Researcher, boloboff@mail.ru
Plaschinsky A. A., Postgraduate, SlavaPlash@yandex.ru

Vinacomin – Institute of Energy & Mining Mechanical Engineering (IEMM) (Hanoi, Vietnam):

Le-Thanh B., Senior Researcher

Based on the assumption that destruction of a rock fragment upon impact is conditioned upon the achievement by the emerging crack of any of the free surfaces of the fragment, the propagation velocity of a fracture crack v_cr was estimated experimentally and by calculation using granite samples of the Vyborg massif. In the experimental setup, impacts at various points on the horizontal surface of granite fragments enabled establishing the most effective impact distance h = l_eff from the edge of their lateral surface, at which the impact breaks off the largest piece of rock. The dependence of this value on the diameter d of the flat face of the ram tester was established; an analysis of the shapes of the resulting broken-off fragments indicated mutual proximity of the values of their geometric parameters; their dependence on d and the length of the fracture crack l_cr were established by calculating the arithmetic mean of these parameters. Such single impact indicators as the rock resistance force N_m, contact stress σ_c, penetration α_p of the ram tester into the rock, and impact duration tm, were calculated; their dependence on d was established. The calculated values of tm were used to calculate the fracture crack propagation velocity v_cr. The latter is close to 11 m/s for all granite fragments, regardless of the values of d and t_m, which is significantly lower than the values established in other studies. This is due to significant differences in the medium being fractured and in the impact velocity.

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